Xiaozhi Wu

Edge dislocation core structures in FCC metals determined from ab initio calculations combined with the improved Peierls–Nabarro equation

We have employed the improved Peierls–Nabarro (P–N) equation to study the properties of 1/2110 edge dislocation in the {111} plane in face-centered cubic (FCC) metals Al, Cu, Ir, Pd and Pt. The generalized-stacking-fault energy surface entering the equation is calculated by using first-principles density functional theory (DFT). The accuracy of the method has been tested by calculating the values for various stacking fault energies that favorably compare with previous theoretical and experimental results. The core structures, including the core widths of the edge and screw components, and dissociation behavior have been investigated. The dissociated distance between two partials for Al in our calculation agrees well with the values obtained from numerical simulation with DFT and molecular dynamics simulation, as well as experiment. Our calculations show that it is preferred to create partial dislocations in Cu, and easily observed full dislocations in Al, Ir, Pd and especially Pt.

The third-order elastic moduli and pressure derivatives for AlRE (RE = Y, Pr, Nd, Tb, Dy, Ce) intermetallics with B2-structure: A first-principles study

Abstract The third-order elastic moduli and pressure derivatives of the second-order elastic constants of novel B2-type AlRE (RE=Y, Pr, Nd, Tb, Dy, Ce) intermetallics are presented from first-principles calculations. The elastic moduli are obtained from the coefficients of the polynomials from the nonlinear least-squares fitting of the energy–strain functions. The calculated second-order elastic constants of AlRE intermetallics are consistent with the previous calculations. To judge that our computational accuracy is reasonable, the calculated third-order constants of Al are compared with the available experimental data and other theoretical results and are found to have good agreements. In comparison with the theory of the linear elasticity, the third-order effects are very important with the finite strains which are lager than approximately 3.5%. Finally, the pressure derivatives have been discussed.

First-principles calculations on temperature-dependent elastic constants of rare-earth intermetallic compounds: YAg and YCu☆

we present the temperature-dependent elastic constants of two ductile rare-earth intermetallic compounds YAg and YCu with CsCl-type B2 structure by using a first-principles approach. The elastic moduli as a function of temperature are predicted from the combination of static volumedependent elastic constants obtained by the first-principles total-energy method with density functional theory and the thermal expansion obtained by the first-principles phonon calculations with density-functional perturbation theory. The comparison between our calculated results and the available experimental data for Ag and Cu provides good agreements. In the calculated temperature

Ab initio study of the thermodynamic properties of rare-earth-magnesium intermetallics MgRE (RE=Y, Dy, Pr, Tb)

0-1000K

Theoretical calculation of the dislocation width and Peierls barrier and stress for semiconductor silicon

, the elastic constants of YAg and YCu follow a normal behavior with temperature that those decrease with increasing temperature, and satisfy the stability conditions for B2 structures. The Cauchy pressure for YAg and YCu as a function of temperature is also discussed, and our results mean that YAg and YCu become more ductile while increasing temperature.

The discrete correction of the core structure for the \langle 100\rangle \{010\} edge dislocation in bcc Fe

We have performed an ab initio study of the thermodynamical properties of rare-earth–magnesium intermetallic compounds MgRE (RE=Y, Dy, Pr, Tb) with B2-type structures. The calculations were carried out in the framework of density functional theory and density functional perturbation theory in combination with the quasiharmonic approximation. The phonon-dispersion curves and phonon total and partial density of states have been investigated. Our results show that the contribution of RE atoms is dominant in phonon frequency, and this character agrees with the previous discussion by using atomistic simulations. The temperature dependence of various quantities such as thermal expansion, bulk modulus and heat capacity is obtained. Electronic contributions to the specific heat are discussed, and are found to be important for the calculated MgRE intermetallics.

First-principles calculations of phonon and thermodynamic properties of AlRE (RE = Y, Gd, Pr, Yb) intermetallic compounds

The dislocation width and Peierls barrier and stress have been calculated by the improved Peierls-Nabarro (PN) theory for silicon. In order to investigate the discreteness correction of a complex lattice quantitatively, a simple dynamics model has been used in which interaction attributed to a variation of bond length and angle has been considered. The results show that the dislocation core and mobility will be corrected significantly by the discrete effect. Another improvement is considering the contribution of strain energy in evaluating the dislocation energy. When a dislocation moves, both strain and misfit energies change periodically. Their amplitudes are of the same order, but phases are opposite. Because of the opposite phases, the misfit and strain energies cancel each other and the resulting Peierls barrier is much smaller than that given by the misfit energy conventionally. Due to competition between the misfit and strain energies, a metastable state appears separately for glide 90° and shuffle screw dislocations. In addition, from the total energy calculation it is found that besides the width of dislocation, the core of a free stable dislocation may be different according to where the core center is located. The exact position of the core center can be directly verified by numerical simulation, and provides a new prediction that can be used to verify the validity of PN theory. It is interesting that after considering discrete correction the Peierls stress for glide dislocation coincides with the critical stress at low temperature, and the Peierls stress for shuffle dislocation coincides with the critical stress at high temperature. The physical implication of the results is discussed.

The Peierls stress of the moving \frac {1}{2}\langle 111\rangle \{110\} screw dislocation in Ta

The core structure of the edge dislocations in body-centered cubic (bcc) crystal Fe has been investigated by the modified Peierls–Nabarro (P–N) equation which includes the discrete correction. An analytical expression of the dislocation solution of the dislocation equation has been obtained by using the truncation approximation. It is found that the dislocation width is nearly doubled by the discrete effects and the agreement between the theoretical prediction and the numerical simulation is improved remarkably.

Surface Effects on the Properties of Screw Dislocation in Nanofilms

The phonon and thermodynamic properties of aluminum–rare-earth (AlRE, RE = Y, Gd, Pr, Yb) intermetallics with B2-type structure are investigated by performing density functional theory and density functional perturbation theory calculations within the quasiharmonic approximation. The phonon spectra and phonon density of states, including the phonon partial density of states and total density of states, are discussed. Our results demonstrate that the density of states is mostly composed of Al states at high frequency. The temperature dependences of various quantities such as thermal expansion, heat capacities at constant volume and pressure, the isothermal bulk modulus and the entropy are obtained. The electronic contribution to specific heat is discussed, and the present results show that the thermal electronic excitation affecting the thermal properties is inessential.

The mechanical and electronic properties of Al/TiC interfaces alloyed by Mg, Zn, Cu, Fe and Ti: First-principles study

The Peierls stress of the moving [Formula: see text] screw dislocation with a planar and non-dissociated core structure in Ta has been calculated. The elastic strain energy which is associated with the discrete effect of the lattice and ignored in classical Peierls-Nabarro (P-N) theory has been taken into account in calculating the Peierls stress, and it can make the Peierls stress become smaller. The Peierls stress we obtain is very close to the experimental data. As shown in the numerical calculations and atomistic simulations, the core structure of the screw dislocation undergoes significant changes under the explicit stress before the screw dislocation moves. Moreover, the mechanism of the screw dislocation is revealed by our results and the experimental data that the screw dislocation retracts its extension in three {110} planes and transforms its dissociated core structure into a planar configuration. Therefore, the core structure of the moving [Formula: see text] screw dislocation in Ta is proposed to be planar.